Drug delivery is a scientific and pharmaceutical field that encompasses the design, synthesis, and use of products that deliver drugs to patients. Goals for such products can include, targeting a drug to a particular location in the patient, protecting a drug against premature degradation, diminishing adverse side effects of a drug, and sustained release of a drug. Polymeric micelles are products that have been pursued as drug delivery vehicles. Polymeric micelles are small, spherical particles (<200 nm in diameter) made up of polymer chains. The polymer chains of polymeric micelles are block copolymers (i.e., typically linear polymers that are composed of repeating blocks of two polymers that differ in hydrophilicity, charge or polarity). Some block copolymers that are amphiphilic block copolymers self-assemble into micelles when placed in an appropriate solvent.
Self-assembled polymeric micelles represent one of the most promising, versatile platforms for drug delivery. Their nanostructural features, such as thermodynamic stability, size, and shape of self-assemblies, can be widely manipulated depending on both amphiphilicity of materials and fabrication techniques. Self-assembly is a process in which a stable ordered ensemble of molecules is formed through the balancing of attractive and repulsive forces between amphiphiles at a concentration above the critical micelle concentration (CMC).[1] One of the most promising types of block copolymers capable of self-assembling is the dendron-coil (DC),[2] A DC is comprised of a flexible linear polymer dendronized at one end in which amphiphilicity can be engineered through the appropriate choice of hydrophilic and hydrophobic blocks. The highly branched, controlled molecular architecture of the dendron allows the unique properties of dendrimers such as monodispersity, precise control of peripheral functional groups, and multivalency to be integrated.[3]
Many groups have reported amphiphilic DCs and other dendron-based copolymers capable of self-assembling into a wide variety of morphologies.[2] Particularly, amphiphilic DCs containing a single hydrophobic peptide block and multiple hydrophilic blocks combined through mediation by a dendron have been shown to preferentially self-assemble into spherical micelles with sizes less than 100 nm.[4]
Over the past decade, significant advances have been made in the development of polymeric micelles to treat and detect cancer effectively[5] and various design strategies have been implemented to enhance cancer targeting.[6,7] The hydrophilic-lipophilic balance (HLB) between polymer chains is a crucial factor used to describe the self-assembly behavior of polymers and is strongly associated with the degree of micellar dissociation and blood circulation time augmenting the enhanced permeability and retention (EPR) effect. In addition, by controlling the HLB it has been shown that a variety of morphologies can be induced (e.g. vesicular, spherical, cylindrical micelles) via self assembly as a result of the interplay between thermodynamic forces.[8] A well-defined density of targeting ligands on the surface and their adopted geometry are also important to produce enhanced selective binding to cancer tissues as supported by recent studies on multivalent cancer targeting.[9,10] In this regard, a dendron, a segment of a dendrimer, is a unique material that not only retains the properties of its parent dendrimer (symmetry and monodispersity) but through distinctive chemical modifications of its focal point and periphery can be hybridized with other materials to create amphiphilic structures that self-assemble and exhibit unique biological responses[11].
In Oerlemans et al. 2010[5], the authors review research and clinical trials on polymeric micelles in anticancer therapy. In Table 1 on page 2571, the review article reports that five micelle products for anticancer therapy had been investigated in clinical trials, one of which (Genexol-PM) has been granted FDA approval to be used in patients with breast cancer. In Table VII on page 2583, the review article lists various multifunctional micellar formulations, including a EGF-receptor-targeted PEG-b-PCL micelles labeled with 111I and a micellar formulation consisting of folate-conjugated PEG-b-PCL loaded with doxorubicin and SPIONS, that combine two or more the functions of targeting ligands, imaging agents and triggered release. At the end of its “Conclusion and Future Perspectives” section on page 2583, the authors state that “the versatility of micelle-based drug delivery and the large number of promising preclinical studies describing numerous approaches to optimize these nanomedicines will bring the development of a magic bullet a major step forward. Now it is time to bring this potential into clinical practice.”
Detecting and/or capturing cells is another field that is important for cancer medicine. For example, although recent advances in diagnostic and therapeutic methods to treat primary tumors have resulted in a decrease in mortality from cancer over the past two years, metastasis of cancer still poses a great challenge as patients often relapse. Disseminated and Circulating tumor cells (DTCs and CTCs respectively) are known to induce secondary tumor formation at distant sites from primary tumors, known as metastasis. Research efforts on diagnosis and prognosis of metastatic cancer have been concentrated on detection of DTCs in bone marrow (BM) and CTCs in blood. Detection of DTCs requires aspiration of BM—a process that is invasive, time-consuming, and often painful for the patients, precluding repeated samplings that are necessary for prognosis studies along with therapeutic treatments. Consequently, effective detection of CTCs in peripheral blood of cancer patients holds a promise as an alternative due to its minimal invasiveness and easy sampling (i.e., blood drawing). However, the detection of CTCs has not yet been implemented for routine clinical practice. Unlike DTCs in BM that are relatively easy to enrich using Ficoll-based assays or the OncoQuick approach, or other immunomagnetic enrichment procedures, CTCs are extremely rare (estimated to be in the range of one tumor cell in the background of 106-109 normal blood cells), presenting a tremendous challenge for efficient, clinically significant detection of CTCs.
Thus, there exists in the art a need for products and methods to efficiently detect and/or capture circulating tumor cells, and to deliver drugs to target cells.